An injury to which region would interfere with the sleep-wake cycle?

The question you should make in order to answer this question, is what controls the sleep-wake cycle?

Well, we all know that the sleep-wake cycle is controlled by nonother than our brain. And if you want to know which region of the brain controls it, it's the  hypothalamus which shuts down certain signals in our brain, causing it to enter "sleep-mode".

Hope it helped,

BioTeacher101